According to the examination by the inventors of the present invention, the techniques as follows are known as the technique for improving the waveform quality of a signal.
For example, Japanese Patent Application Laid-Open No. 4-207224 discloses an output circuit which enables the signal transmission, in which impedance matching between the output circuit and a transmission path is achieved. The configuration of the circuit includes a MOS transistor in an output stage, a MOS transistor and a current source combined with the MOS transistor in an output stage to form a current mirror circuit, and the like. More specifically, this output circuit sets an output impedance by passing a predetermined bias current to the MOS transistor in an output stage by the use of a current mirror circuit so as to achieve the impedance matching between the output circuit and the transmission path.
Also, Japanese Patent Application Laid-Open No. 5-276004 discloses an output circuit capable of reducing the ringing in an output waveform. The configuration of the circuit includes an output driver circuit, voltage control means connected to a transmission terminal of the output driver circuit, and the like. The output driver circuit has a driving capability corresponding to the transient state period of a signal, and the voltage control means has a function to switch the output resistance by a plurality of damping resistors. More specifically, this output circuit is designed to reduce the ringing in an output waveform by optimally controlling the driving capability and the damping resistors.
Also, Japanese Patent Application Laid-Open No. 11-345054 discloses a driver circuit for signal transmission capable of preventing the waveform distortion. The configuration of the circuit includes an output driver, a front-stage driver for driving the output driver, means for adjusting the output level of the front-stage driver, and the like. More specifically, this driver circuit is characterized in that the output level is emphasized in advance in an output stage so as to cope with the attenuation of the high-frequency components in a transmission path.
Also, Japanese Patent Application Laid-Open No. 2003-8423 discloses a bus interface circuit capable of reducing the distortion in a signal waveform. The configuration of the circuit includes a circuit for detecting the change of a signal in a connector terminal to a bus, a circuit for driving the connector terminal in a direction identical to the direction of the change in accordance with the detected change of a signal, and the like. More specifically, this bus interface circuit is designed to operate so that the voltage level on a bus can always be the same level as the voltage level of the connector terminal, thereby preventing the influence of the connector terminal on the signal transmitted on the bus.
Also, Japanese Patent Application Laid-Open No. 2-177722 discloses an output circuit for reducing the output noise. This output circuit is provided with two output circuits of the same configuration, and the ringing in output potential and the like are reduced by operating the two circuits alternately.